Infrared (IR) staring sensors are well known in the prior art for obtaining data in the IR spectrum. Typically, these sensors include an optical train that minimizes the optical blur spot at the focal plane. The optical train receives the optical rays through an aperture, and then directs the incoming IR optical rays onto a focal plane array (FPA) for further processing and display by other components of the device. One of the disadvantages of these devices, however, is that during operation, a portion of the incoming IR radiation actually reflects off the focal plane array, passes back through the optical device and leaves the device through the aperture as an IR emission signal. This phenomenon is known as retro-reflectivity.
It is desirable that the retro-reflectivity for the device be minimized, so that the IR staring sensor is undetectable during operation of the device. One such device that minimizes the retro-reflectivity of IR staring sensors is described in U.S. Pat. No. 6,862,147 issued on Mar. 1, 2005 to Sonstroem, which is incorporated herein by reference.